Two miners survived Monday's explosion in Chongqing, western China, but rescuers working around the clock found no others alive, state media said.

All bodies have been recovered and rescuers were shown bowing their heads in memorial for the dead.

Gas explosions inside mines are often caused when a flame or electrical spark ignites gas leaking from the coal seam. Ventilation systems are supposed to prevent gas from becoming trapped.

The State Administration of Work Safety ordered an investigation, saying those responsible must be strictly punished. Local officials also ordered smaller mines to shut down temporarily.

The country's mining industry has long been among the world's deadliest and the head of the State Administration of Work Safety said earlier this year that struggling coal mines might be likely to overlook maintenance.

China is the world's largest producer and consumer of coal but there are plans to shut more than 1,000 outdated mines in a broader plan to reduce over-production.